Computer programs are typically sold in the form of executable modules. An executable module contains instructions that have been compiled and translated into machine code so that they can be loaded into memory and executed. After software manufacturers create an executable module, they make multiple copies of the executable module and then sell the copies to purchasers. While making the copies, software manufacturers typically insert a unique serial number at a predetermined location within each copy of the executable module. The serial number is a unit of data that distinguishes each copy of the executable module. If a subsequent copy is made of the purchased copy, the subsequent copy should bear the same serial number as the purchased copy.
When a purchaser purchases a copy of the executable module, the purchaser's name and the serial number of the purchased copy are typically registered with the software manufacturer. This registration may be accomplished by the purchaser submitting a registration form to the software manufacturer or, in some instances, the software manufacturer or a retail vendor recording the necessary information at the time of purchase. By associating a serial number with each purchaser, software manufacturers hope to deter unauthorized copying. By comparing the serial number of a copy in question with the software manufacturer's list of recorded serial numbers, the software manufacturer may determine whether the copy in question is an authorized copy. If the software manufacturer determines that the copy in question is an unauthorized copy, the serial number within the unauthorized copy may indicate from which authorized copy the unauthorized copy was derived.
Unfortunately, the purchaser (or someone who has access to the authorized copy) may easily remove or alter the serial number, make multiple unauthorized copies, and then distribute or even sell the unauthorized copies to third parties. The software manufacturer is able to identify such copies as unauthorized, but, without a valid serial number to rely on, the software manufacturer is unable to determine the origin of the unauthorized copies. Similarly, when a purchaser fails to register the serial number of a purchased copy with the software manufacturer, the software manufacturer may later be unable to determine whether the serial number of the purchased copy has been altered.
Software manufacturers require a method of including a serial number or other identifying mark within a copy of an executable module in such a way that the serial number or identifying mark cannot be easily removed or altered. Additionally, software manufacturers require a method of analyzing a copy of an executable module to determine its serial number or identifying mark.